A bug from queryset-refactor days: although the Query class has "grou…

…p_by" and
"having" attributes, only the former was included in the resulting SQL, meaning
subclasses had to completely duplicate Query.as_sql() if they were using any
kind of grouping filtering on the results.
git-svn-id: http://code.djangoproject.com/svn/django/trunk@9007 bcc190cf-cafb-0310-a4f2-bffc1f526a37